Camera-based optical tactile sensors can be very sensitive to shear because they transduce deformation of the soft sensor surface into a lateral image. For optical tactile sensors such as the TacTip biomimetic optical sensor used here [1]}, [2]} and other marker-based sensors [3]}, [4]}, the surface shear will also distort the apparent geometry of the contact. This distortion is because the normal indentation is represented in the local shear strain of the markers, upon which the global shear strain is superimposed. This contrasts with optical tactile sensors that reconstruct the indentation field from reflection, such as the GelSight [5]}, where shear will shift the imprint on the tactile image but otherwise the imprint shape should be relatively unaffected.
